This invention relates generally to an electronic tuning type radio receiver having a scan control for automatically stopping the so-called local oscillation frequency scanning operation at its optimum tuning point, and more particularly to an improved electronic tuning radio receiver in which AM reception and FM reception share a common circuit for providing a tuning signal for the scan control and automatically discontinuing the scanning operation at its optimum tuning point. The conventional electronic tuning radio receiver tunable to both FM and AM broadcasting stations includes two separate local oscillators one for FM reception and the other for AM reception, each of which has a different local oscillation frequency. This is due to the fact that the intermediate frequency for FM reception is totally different from that for AM reception. For the type of radio receivers which automatically scan the local oscillation frequency, the scan rate is set at a relatively low level to enable the operator to manually stop the automatic scanning operation on the local oscillation frequency at the optimum tuning point. Radio receivers with the capability of automatically stopping the automatic scanning operation on the local oscillation frequency can accomplish a simple and quick tuning operation but needs complicated circuitry for the purpose of automatically stopping the scan operation.
It is well known that such automatic stop circuitry is adapted to take advantage of the intermediate frequency output of an intermediate frequency circuit. To this end it requires two separate automatic stop circuits for FM reception and AM reception due to the fact that the respective intermediate frequencies for FM reception and AM reception are quite different from each other, for example, 10.7 MHz and 450 KHz in Japan.
The automatic stop circuitry is very convenient for radio receivers with the capability of automatically scanning the local oscillation frequency to acheive optimum reception of any desired broadcasting station, that is, prompt, accurate and simple reception. However, such circuitry has the problems in that the circuit arrangement is complex and the two separate stop circuits should be incorporated into the radio receivers independently of each other for FM reception and AM reception. As a matter of fact, the use of the automatic stop circuitry is confined to expensive radio receivers.